7 Summary and conclusions

The sample of spectrally hard X-ray sources in the field of the LMC observed with the ROSAT PSPC and published in the catalog of HP99 has been reinvestigated. Especially accurate values for the count rate have been determined in the spectrally hard (0.5-2.0 keV) and broad (0.1-2.4 keV) band respectively and values for the hardness ratios $H\!R1$ and $H\!R2$ have been determined making use of merged data in the direction of each investigated X-ray source. The analysis has been restricted to X-ray sources which have been observed in the inner 20$\arcmin$ of the PSPC detector.

Simulations have been performed to derive tracks for powerlaw spectra with slopes comprised by X-ray binaries and AGN in the $H\!R1$ - $H\!R2$ plane. In these simulations a wide range of metallicities for the LMC gas has been considered. Comparing the location of the X-ray sources in the $H\!R1$ - $H\!R2$ plane with respect to the simulated tracks for X-ray binaries and AGN a source classification has been achieved of the sample of spectrally hard X-ray sources observed in the central 20$\arcmin$ of the PSPC detector. 141 sources have been classified as AGN (or as likely AGN) and 30 sources as X-ray binaries (or as likely XRB). This means that 82% of the classified hard X-ray sources in the LMC field are AGN and 18% are X-ray binaries.

I constrained, for 31 of these AGN (18 in addition to sources already investigated in Paper I), the LMC gas columns from the location of these sources in the $H\!R1$ - $H\!R2$ plane. In addition I derived for 54 AGN upper limits for the LMC gas columns.

I independently constrained the metallicity of the LMC gas by fitting simulated tracks of constant powerlaw slopes in the $H\!R1$ - $H\!R2$ plane to the observation derived $H\!R1$ and $H\!R2$ values for the AGN and the X-ray binary sample. I found that the required metallicity of the LMC gas is in the range -0.6 to +0.1 dex at 99% confidence.

I also established the catalog of X-ray sources in a deep merged observation of the field of the supergiant shell LMC 4. I detected 97 X-ray sources of which I classified 35 sources as candidate AGN.

The number of 30 (candidate) X-ray binaries observed in the LMC is compared with the number of X-ray binaries predicted from population synthesis calculations for the LMC. In addition the number of (candidate) high-mass X-ray binaries observed in the LMC with luminosities in excess of $10^{36}\ {\rm erg}\ {\rm s}^{-1}$ is compared with the number of high-mass X-ray binaries in the SMC. It is found that the comparable number of high-mass X-ray binaries scale with the comparable gas mass of the host galaxies. The number of high-mass X-ray binaries may have been preferentially enhanced in the SMC due to a star formation burst initiated by the LMC-SMC galaxy encounter.